1. Field of the Invention
The invention relates to a magnetic resonance apparatus, comprising a magnet system for generating a steady magnetic field in a measurement space, a coil system for generating gradient fields in the measurement space, and at least one RF coil which is accommodated in a housing which can be arranged in the measurement space and which is also suitable to accommodate an object to be examined, the apparatus also comprising a jig for positioning an instrument to be introduced into the object to be examined, which jig comprises a first stop for defining the position of a free end of the instrument in a first coordinate direction of a three-dimensional system of coordinates.
2. Description of the Related Art
An apparatus of this kind is known from U.S. Pat. No. 5,155,435. In the known apparatus the jig comprises a guide which is connected to the frame of the apparatus via a number of ball joints and adjustable connection means and which serves to guide the instrument which may consist of, for example a needle for carrying out a biopsy. The object to be examined, for example a part of the body of a patient, must first be introduced into the apparatus in order to form an image thereof in the absence of the instrument. This image is stored in a memory, after which the patient is removed from the apparatus. Using this image, the desired position of the instrument is determined and the jig is adjusted accordingly. Subsequently, the patient is introduced into the apparatus again; the position of the patient must be accurately the same as during the formation of the first image. Finally, using the jig, the instrument is introduced into the part of the body to be examined, it then being possible, if desired, to make a second image. This procedure is time-consuming and comparatively strenuous to the patient, because the patient must be moved into and out of the apparatus a few times. Moreover, very high requirements are imposed in respect of the accuracy with which the patient is positioned when introduced into the apparatus for the second time.